Fluid power transmission



Jan. 17, 1961 E. c. MILBERGER ETAL 2,968,625

FLUID POWER TRANSMISSION Filed July 25, 195e IOw DSS LISOOSIA IOON Own I OOO.

INVENTORS. ERNEST C. MILBERGER 8 SAMUEL M. DARLING BY MM( qLjQLa/VQ eil' ATTORNEYS.

FLUID POWER TRANSMISSION Ernest C. Milberger, Maple Heights, and Samuel M. Darling, Lyndhurst, Ohio, assignors to The Standard Oil Company, Cleveland, Ohio, a corporation of Ohio Filed July 25, 1956, Ser. No. 600,024

2 Claims. (Cl. 252-75) This invention relates to uid power transmission and to a power transmission fluid characterized by an ASTM slope below 0.3, comprising a light mineral oil of normal viscosity index, and an inorganic gelling agent and im idazoline in amounts to impart an ASTM slope of below 0.3 to the mineral oil.

Petroleum oils have certain performance characteristics which make them particularly suitable for use as power transmission fluids. A power transmission Huid which is well suited for the job -for which it is intended must have good flowability and pumpability, lubricating ability, chemical stability, rust-inhibiting ability, demulsibility, and defoaming ability. All of these characteristics are important, and should be displayed over the entire range of temperatures at which the system is to be used. All liuids, however, undergo a ,change in viscosity with temperature. The rate of change of viscosity with change in temperature which characterizes petroleum oils is not as low as that for many synthetic oils such as silicone oils `and the Ucon oils, which are polypropylene glycol ethers, and this is a disadvantage.

The rate of change in viscosity with temperature of petroleum oils ordinarily is measured by the viscosity index, usually abbreviated V.I. The higher the V.I., the lower the rate of change in viscosity, and the better the petroleum oil for use as a hydraulic fluid. However, the viscosity index loses its sensitivity as a characterizing property when the oil has an exceptionally low rate of change in viscosity, of the order of that which characterizes many synthetic oils. A viscosity temperature relationship has been developed which is superior to the viscosity index for this type of petroleum oil. This is the ASTM slope, :adopted as a standard method by the American Petroleum Institute, Standard 533-43, ASTM designation D-341-43. This slope is the tangent of the acute angle of the viscosity-temperature,plot of the oil on the ASTM standard chart D34l-43. The smaller the ASTM slope, the flatter the curve, and the lower the change in viscosity with temperature.

Typical ASTM slopes of a number of petroleum and synthetic oils are given below:

Petroleum Oils Viscosity, SSU, ASTM 100 F. 210 F. Slope Straw Parafln 74. 1 36.6 0.78 Automatic Transmission Fluid 200 Y 50 0.66 Synthetic Oils:

Silicone Oils- Dow Corning 550 440 101 0, 45 General Electric 9981-LT-125... 577 231 0.23 Ucon Oils l- LB 885 385 75.1 0. 55 LB 525 525 93. 1 0. 51 LB G50-X 650 106 0. 51 Estere- Bis-(Z-ethylhexyl) sebscate 67. 8 37 0. 70 Bis(3,5.5-trimethylhexy1) sebacate- 94. 6 41. 3 0. 65

1 Monobutyl No. 2,615,853.

ate

7 poly 1,2-oxy propylene glycols. See Kirkpatrick U.S.'

2,968,025 Patented Jari. 17, 1961 The lighter mineral oils of low viscosity would be especially suitable for use as power transmission media because of their low sludge and deposit-forming tendencies compared to the heavier oils. However, light oils lack lubricating ability under operating conditions, and ASTM slope is in most instances too high. ln fact, the light oils have such a low viscosity at high temperatures that they are not suited without modification for such purposes.

In accordance with this invention, power transmission fluids are provided having a viscosity within the range from to 1000 SSU at 100 F. and from 50 to 750 SSU at 210 F., and an ASTM slope below about 0.3, employing as the base oil light lubricating oils having a viscosity of about 50 to 300 SSU at 100 F. and from 25 to 55 SSU at 210 F. The ASTM slope of the light lubricating oils is not critical because the power transmission fluids of the invention nonetheless have an ASTM slope of less than 0.3, considerably less than many synthetic oils and most ordinary petroleum hydrocarbon oils, even when highly refined, as the above table shows.

The power transmission fluids of the invention comprise from 1 to 3% based on the weight of the oil of au inorganic gelling agent, and from about 1% to about 20% by weight of the gelling agent of an imidazoline having an aliphatic radical of from 8 to 20 carbon atoms. These two additives in combination increase the viscosity of the light oil to the point Where the composition has a vis- `cosity suitable for a power transmission uid, and in addition improve the ASTM slope of the base oil to below 0.3. The compositions of the invention are tluid under all conditions of use at normal and elevated temperatures.

These effects are not obtained in the absence of either the inorganic gelling agent or the imidazoline. The increase in the viscosity and decrease in the ASTM slope due to the inorganic gelling agent are relatively small. The imidazoline alone has no effect upon viscosity or ASTM slope. However, in the presence of the inorganic gelling agent the imidazoline eiects a further increase in viscosity, and a further decrease in the ASTM slope. Thus, the imidazoline makes it possible to achieve higher viscosities and lower ASTM slope within the desired ranges, using lesser amounts of the inorganic gelling agent. The viscosity-increasing and ASTM slope decreasing effects of the imidazoline are obtained after the mixture of oils, gelling agent and imidazoline has been heated to temperatures of 300 F. or higher.

The lubricating oil stock used in preparing the compositions of the invention will have a viscosity within the range from 50 to 300 SSU at 100 F. and 25 to 55 SSU at 210 F. The base stock is preferably a lubricating oil fraction of petroleum and it may be unrefined, acidreiined or solvent-refined, as required for the particular lubricating need. The nature of the base oil makes little difference in the relative consistencies of the compositions, although conventionally acid-refined oils produce slightly thicker uids than the solvent-refined oils. The viscosity index of the oil is not critical.

The inorganic gelling agent can be any inorganic material which is dispersible in the oil and which is so finely divided as to be nonabrasive. The preferred materials are the aerogels which can be formed from any material not incompatible with the oil, such as silica, alumina and magnesia. Other gel-forming metal oxides, hydroxides and suliides can be used, of which attapulgite, the bentonites (such as Wyoming bentonite, montrnorillonites and hectorite), beidellite, saponite, nontronite, sepiolite, biotite, vermiculite and zeolites, synthetic clays such as magnesia-silica-sodium oxide, lime-silica-potassium oxide and haria-silica-lithium oxide are exemplary, as well as synthetic zeolites, of which the complex aluminum silicates `are exemplary. e

A series of silica aerogels which can be used as the inorganic gelling agent of the invention are manufactured by Monsanto and marketed under the trade name Santocel.

Santocel C is prepared from an alkali silicate solution. Silicio acid dissolves'in caustic alkali such as sodium hydroxide andthe alkali silicates, such as sodium silicate, can be obtained from various natural minerals and clays or by fusing silicon dioxide with alkali hydroxides or carbonates. Fused alkali silicates such as water-glass, sodium tetrasilicate (Na2Si4O9) C an be completely dissolved on long heating with water, but the result is not a solution o f the silicate as such but of silicic acid peptized by alkali as, well asy free alkali. By addition of an acid to 'such' a solution, for example, an inorganic acid such as sulphric acid, hydrochloric acid or carbonic acid, or an'organic acid such asv acetic acid, oxalic acid or formic acid, the silicic acid is precipitated in the form of a gel which is called a hydrogel or aquogel. The structure of this gel has not been fully elucidated but it is, generallyfaccepted that it is composed of a honeycomb structure of, the silicon dioxide Si02 within the pores of which is` enclosed the aqueous solution remaining after precipitation of the silicic acid. Thus, it can be generally stated` that these hydrogelscan be obtained starting from any water-'soluble alkali silicate, including not only water glass as mentioned above but sodium metasilicate Na2SiOs,'sodium metasilicate nonahydrate Na2SiOs9H2O and sodium d isilicate NazSizOs. All of these silicates are soluble in water, in which they decompose to form silicic acid Solarien.

Such an aqueous solution of silicic acid will contain sufficient S iO2 in solution to form a hydrogel containing within'the range from 3%v to about 12% silica as SiO2, after gel formation by addition ofthey acid. The amount of silica can readily be calculated, depending upon the amount'of acid which4 is required to acidify the solution andwhetherthe acid employed is concentrated or diluted. It'rslnot necessary to characterizerthe silicic acid solution invt'erms of the alkali content calculated either as Na2O or NaOHfinasmuch as this forms a salt with the anion ofthe acid. employed and is washed out of the aquogel at the time of alcogel formation.

After formation of the aquogel, the gel is Washed free from salts` and excess acid, and then converted to an alcogel byy soaking in ethyl alcohol or some other watersolublel volatilejaliphaticV alcohol. Several portions of the alcoholmay Vbe'lnecessary completely to removerthe aque; ous solution The resultinglalcogel then is placed in an autoclave. In order to remove the liquid phase without avcollapse of the gel s tructure,the autoclave is heated at a temperature above the critical temperature of thealcohol, and the, pressure is allowed to increase to a point above the critical pressure of the alcohol. The vent valve iswthen openedand the alcohol allowed to escape. Under thesehconditions thesilicagel structure remains practically'undisturbed and the liquid phase of the gel is replacedwith air. The material is then reduced in particle size by blowing it through a series of pipes containing sharp Vbends with jets of compressed air. Santocel C has a secondary particle size of about threeto five microns.

Santocel A is prepared as set forth for Santocel C up to thepoint of removal of the product from the autoclave. This material is run through a continuous heating chamber where it is heated for one-half hour to a temperature of about 1500 F. to eliminate the las-t traces of volatile'material. It isrthen broken down in a reductionizer or micronizer to a particle lsize o f about one-sixteenth inch in diameter. The Si02 content of the original hydrogel use d in preparingStantocel C is approximately 9.75%, whereasthat of Santocel A is about 7.0%.

AfRlisa modification of A, differing only in that the materialis reductionized to about the same particle size as. C, approximately three to fiveV microns in diameter. ARD is a modification of AR, diieringonly in that 4 ARD is densied by extracting air under vacuum, and therefore has a slmallervolurne than AR.

AX is an A which has notbeen devolatilized.

CDV is a C which has been devolatilized as set forth for Santocel A. The Santocel is reductionized before being devolatilized.

CDvR differs slightly `from CDV in that the CDVR has been `devolatilizedl just after heating in the autoclave and then reductionized.v It differs from CDv in that the latter reductionized before being devolatilized. Y

The primary differences betweenthe A and@ series are asfollows." Y

(l) The Cs are prepared from a sodium silicate solution containing 25% more silica than the As. Therefore, in general the As" are lighter l'and composed of smaller particles than the Cs.

(2) The As have undergone a devolatilization step in their preparation.

YThe`followingfarel the bulk densities` ofl several of the preferred-Qsilicaaerogels. H 'l i Density, grams per ml. f Y 0.029` n n0.056 to 0.064 L 0 .082

In general, AR and ARD show superior gelling ability and the As. ingeneral` are better thanfthe Cs." Silica, aerogels which have been'devolatilized generally have. a higherA gelling etliciency than the undevolatilizedaerogels... ,n l

Other typesr of inorganic gelling.A agents which may be used include aFumed Silica marketedby B. Goodrich Company.` It isV finely'divided and appears veryl much like "an aerogel. It is'rnade by combustion orvaporization process,` as aV source of white carbon black for the, rubbenindustry. The particles areqseveral microns in size and porousk in nature.

Another material is Linde Silica` Flour marketed by Linde Air Products Co. It is very similar in physical appearance tothe silica aerogel. The particle size of the'silica is purported to be.0.01 to 0.05 micron and the silica is said to b'e manufactured byburning silicon tetraf chloride and 4collectingfthe combustionv producten c ool plates analogous to the production of carbon black. The particles are thought to be aggregates or clusters of particles rather than'of sponge-like character.

Still another inorganic gelling agent known is Ludoxf silica from Du Pont, which is known as a silica sol, and

silica derivatives thereof. Ithasa particle size of the order of 0.01 to 0.03 micron.

The silicasfrom Columbia-Southernalso are useful. These haveythe followingA properties.

Brunauer-Emmett- Teller Mltrogen vAbsorption Surface Wet Screen Retained 325 Mesh, Percent;

'bining them with the oilin a combination with analiphatic g amine ,rather than the use of novel gelling agents pei se.A

HIC--CHa 5 4 where R is hydrogen, alkyl or a hydroxy alkyl radical having from 1 to 18 carbon atoms and R' is an alkyl or alkylene group having from 8 to 20 carbon atoms.

These compounds are prepared by reaction of aliphatic acids and diamine-s followed by cyclization, in the following way:

HzC--CHQ +2H2o R'COOH-l-RNHCHQCHENHr-R-N N C where R and R are the same as in the general formula.

Illustrative R radicals are undecyl, tridecyl, pentadecyl, undecenyl, heptadecyl and heptadecenyl. Illustrative R radicals are ethyl, methyl, propyl, butyl, hexyl, hydroxyethyl, hydroxyisopropyl, hydroxybutyl and hydroxyhexyl.

The imidazoline should be oil-dispersible or oil-soluble and will also be hydrophobic in view of the long-chain aliphatic group at the R position.

The relative proportions of the inorganic gelling agent and the oil will vary somewhat depending upon the desired viscosity in the nal compositions, the gelling ability of the inorganic gelling agent and viscosity of the oil used. Compositions made with the lower viscosity oils require a somewhat larger amount of inorganic gelling agent to give a composition of the same viscosity. The compositions of the invention are uids. In general, the amount of inorganic gelling agent falls within the range of from l to 3% and in most cases preferably would be from 2 to 3%.

The viscosity as might be expected increases in a fairly linear relationship with increase in concentration of the inorganic gelling agent and the amount of gelling agent can be selected in relation to the desired viscosity in view of this.

The concentration of the imidazoline usually will lie within the range from about 1% to about 20%, preferably from 5 to 10%, based on the weight of the inorganic gelling agent, but here again the amount employed will depend upon the increase in stability without an excessive increase in viscosity, the desired amount and nature of the gelling agent and the economics involved. A cheaper compound can of course be used in much larger quantities than an expensive compound at the same total cost as the lubricant.

The composition is made simply by mixing the inorganic gelling agent, the oil and the imidazoline in any order or manner. The imidazoline also can be incorporated with the inorganic gelling agent before mixing with the oil, for example, by dissolving the irnidazoline in a solvent such as pentane, mixing it with the gelling agent and then evaporating the pentane. Such a treating agent can be sold as an article of commerce and dispersed in an oil when the composition of the invention is to be prepared.

Generally, the imidazoline is dispersed in the oil and the inorganic gelling agent added thereto and mixed therewith. Any simple mixing technique can be employed and if desired the mixture can be homogenized in a colloid mill.

The imidazoline must be uniformly distributed in the composition or on the inorganic gelling agent and for this reason the imidazoline is oil-dispersible or oilsoluble or else soluble in some medium in which it can be applied to the gelling agent before incorporating the latter in the oil.

The composition of the invention is not limited to the oil, gelling agent and imidazoline. Any of the materials conventionally added to lubricants can be included. The expression consisting essentially of as used herein is intended to refer to the components which are essential to the composition, that is, the oil, the inorganic gelling agent and the imidazoline, and the expression does not exclude other components from the composition which do not render it unsuitable as a hydraulic iiuid.

The following examples illustrate preferred embodiments of the invention:

Examples 1 to 5 Example No. Percent Irnidazoline Percent Settling None 100. 1 10 6.

gg }Hard cake.

A great increase in stability over the control is noted with an Amine O content of 10% based on the amount of the Santocel. Samples containing 30, 40, 50 and 100% of the Amine O settled to a hard cake on standing. This shows these amounts of Amine O are excessive.

Examples 6 and 7 A second series of compositions was prepared containing 2.5% by weight Santocel AR in the straw parafiin oil of Examples l to 5. One of these samples contained 10% by weight based on the Santocel (0.25% by weight of the oil) of Amine O. After mixing the samples were subjected to high shear and temperature by recycling through a small gear pump and through a steel coil at 400 F. After this treatment, the samples were subjected to further high shear conditions by atomisation through a diesel injector nozzle set at 2500 to 3000 p.s.i.g. Oil was ejected from the nozzle into a iiask and held under partial vacuum to remove entrained air.

The viscosities of these samples were determined in a Stormer viscometer and compared with the viscosity of the base oil:

Percent Amine O Percent Example N o.

None None 78 2. 5 None 270 2. 5 10 360 The data shows that the imidazoline increases the viscosity of the suspension. An oil with a very low ASTM slope is obtained as shown in the drawing which compares the ASTM slope of the oil containing 10% Amine O with the straw paraffin oil. The curve of a 133 VI. oil is included for comparison; its ASTM slope is 0.66.

Settling tests were run on the samples which had been cycled through the gear pump, and subsequently atomised through the diesel nozzle. The atomisation was found to reduce settling to zero.

All parts and percentages in the specication and claims are by weight. Amounts of the imidazoline are by weight of the inorganic gelling agent unless otherwise indicated. Amounts of the inorganic gelling agent are by, weight of theoil.

We claim:

1. In a process for Huid power transmission the improvement which comprises transmitting power by means of a iluid having a viscositywithin the range from 75 to 1000 SSU at 100 F., and from 5,0 to 750 SSU at 210 F., and having an ASTM slope below about 0.3, consisting essentially of a mineralv lubricating oil having a viscosity within the range from 50 to 300 SSU at- 100 F. and from 25 to 55 SSU at 210 F., a silica aerogel inran amount within the range from about 1% to about 3% imparting anY increased viscosity and a decreased ASTM slope to the oil, and from about. 1% to about 20% by weight of the silica aerogel of an aliphatic imidazoline having the following formula:

IRI

where R is selected from the group consistingof'hydro.-Y

gen, alkyl and hydroxyalkyl radicals having from one to eighteen carbon atoms and-R is selected from the group consisting of alkyl and alkylene radicals having from eight to twenty carbon atoms, the imidazoline imparting a further increase in viscosity and a further decrease in ASTM slope, supplementing the eiect of the silica aerogel.

2. A processin accordance with claim 1 in which the imidazoline is 1LIS-hydroxyethyl-Z-heptadecenyl imidazoline. v

References Cited in the tile of this patentl UNITED STATES PATENTS 2,531,440 Jordan Nov. 28, 1950 2,554,222 Stross May 22, 1951 2,655,476 Hughes et al. Oct. 13, 1953 2,711,393 Hughes et al June 2l, 1955 2,766,205 Marshall Oct. 9, 1956 i l I 

1. IN A PROCESS OF FLUID POWER TRANSMISSION THE IMPROVEMENT WHICH COMPRISES TRANSMITTING POWER BY MEANS OF A FLUID HAVING A VISCOSITY WITHIN THE RANGE FROM 75 TO 1000 SSU AT 100*F., AND FROM 50 TO 750 SSU AT 210*F., AND HAVING AN ASTM SLOPE BELOW ABOUT 0.3, CONSISTING ESSENTIALLY OF A MINERAL LUBRICATING OIL HAVING A VISCOSITY WITHIN THE RANGE FROM 50 TO 300 SSU AT 100*F. AND FROM 25 TO 55 SSU AT 210*F., A SILICA AEROGEL IN AN AMOUNT WITHIN THE RANGE FROM ABOUT 1% TO ABOUT 3% IMPARTING AN INCREASED VISCOSITY AND A DECREASED ASTM SLOPE TO THE OIL, AND FROM ABOUT 1% TO ABOUT 20% BY WEIGHT OF THE SILICA AEROGEL OF AN ALIPHATIC IMIDAZOLINE HAVING THE FOLLOWING FORMULA: 